The huchen or Danube salmon (Hucho hucho) is a species of freshwater fish in the salmon family (family Salmonidae) of order Salmoniformes. It is the type species of its genus. Native to the Palearctic ecozone, the huchen occurred originally in the Danube basin in Europe but has been introduced elsewhere on the continent and also in Morocco where huchen doesn't reproduce because of high water temperature. In historic times it occurred also in the Dniestr basin. Sometimes it lives in big dam reservoirs like on big mountain rivers like Czorsztyn Lake in Poland. This food fish is threatened with extinction. Some authors consider the taimen to be a subspecies of the huchen.
The huchen has a slender body that is nearly round in cross-section. On the reddish brown back are several dark patches in an X or crescent shape. Smaller fish feed on the larvae of water insects or on insects dropped into the water; the larger individuals are predators of other species of fish and other small vertebrates such as mice crossing rivers.
This largest permanent fresh water salmonid spawns in April, once water reaches a temperature of 6 to 9 °C (43 to 48 °F). For spawning, the huchen migrates up the river, where females excavate depressions in the gravel in which to deposit the eggs. Larvae hatch 30 to 35 days after fertilisation.
There is now a considerable commercial effort to produce huchen fry to re-introduce the species into the wild. This requires the adults being caught just before spawning and kept in special tanks. Fry are released in appropriate places once they have reached 4 to 10 centimetres (1.6 to 3.9 in).
The world record huchen was 58 kilograms (130 lb), caught by Bosnian angler Halil Sofradžija at Dragojevića Rapids on the Drina river, near the town of Ustikolina in Bosnia and Herzegovina in January 1938. He used rod and reel.